In this book we shall use the now widely accepted System lntemationale (SI) units

of energy. Here the basic unit of energy is a joule. The magnitude of the joule may

be understood from the following examples for various types of energy.

Kinetic energy. A mass of 2 kilograms (4.4 Ib) moving at a velocity of 1 meter per second (3.3 ft/s) has a kinetic energy of 1 joule.

Potential energy. A mass of 0.1 kilogram (3.5 ounces) at a height of 1 meter (3.3 ft) above the earth’s surface has a potential energy of 1 joule.

Chemical energy. Burning 1 kilogram (2.2 Ib) of coal releases approximately

3.5 million joules of energy.

Electrical energy. A 100-watt lamp burning for 1 second uses 100 joules of electrical energy.

Nuclear energy.-. Converting 1 kilogram of mass into energy releases 80 thousand million million joules.

Thermal energy.. Heating 1 kilogram of water by 1 °С (1 .8°F) requires 4187 joules.

The rate of energy flow or production is measured in watts, I watt being I joule of energy per second.

Units such as the joule and the watt are rather small for many practical pur­poses. In the SI system of units the practice is to use prefixes to denote larger quantities. Thus:

1 kilojoule (kj) = 1000 joules 1 megajoule (MJ) = 1 million joules 1 gigajoule (GJ) = 1 thousand million joules 1 terajoule (TJ) = 1 million million joules 1 kilowatt (kW) = 1000 watts 1 gigawatt GW) = 1 thousand million watts

Many other measures of energy are in common use, and it may be helpful to state here the relationship between these units and their SI equivalents:

1 calorie (energy required to heat 1 gram of water by 1 °C)

1 British thermal unit (Btu) (energy required to heat 1 lb of water by 1 °F) 1 therm (100,000 Btus)

1 mtce (energy released by burning 1 million tons of coal)